Add support for Rails 6 in polyamorous

polyamorous/lib/polyamorous.rb

@@ -12,8 +12,8 @@ if defined?(::ActiveRecord)
   require 'polyamorous/swapping_reflection_class'
 
   ar_version = ::ActiveRecord::VERSION::STRING[0,3]
-  ar_version = ::ActiveRecord::VERSION::STRING[0,5] if ar_version >= "5.2"
-  ar_version = "5.2.1" if ::ActiveRecord::VERSION::STRING >= "5.2.1"
+  ar_version = ::ActiveRecord::VERSION::STRING[0,5] if ar_version >= "5.2" && ::ActiveRecord::VERSION::STRING < "6.0"
+  ar_version = "5.2.1" if ::ActiveRecord::VERSION::STRING >= "5.2.1" && ::ActiveRecord::VERSION::STRING < "6.0"
 
   %w(join_association join_dependency).each do |file|
     require "polyamorous/activerecord_#{ar_version}_ruby_2/#{file}"

polyamorous/lib/polyamorous/activerecord_6.0_ruby_2/join_association.rb

@@ -0,0 +1,2 @@
+# active_record_6.0_ruby_2/join_association
+require 'polyamorous/activerecord_5.2.1_ruby_2/join_association'

polyamorous/lib/polyamorous/activerecord_6.0_ruby_2/join_dependency.rb

@@ -0,0 +1,81 @@
+# active_record_6.0_ruby_2/join_dependency.rb
+
+module Polyamorous
+  module JoinDependencyExtensions
+    # Replaces ActiveRecord::Associations::JoinDependency#build
+    def build(associations, base_klass)
+      associations.map do |name, right|
+        if name.is_a? Join
+          reflection = find_reflection base_klass, name.name
+          reflection.check_validity!
+          reflection.check_eager_loadable!
+
+          klass = if reflection.polymorphic?
+            name.klass || base_klass
+          else
+            reflection.klass
+          end
+          JoinAssociation.new(reflection, build(right, klass), name.klass, name.type)
+        else
+          reflection = find_reflection base_klass, name
+          reflection.check_validity!
+          reflection.check_eager_loadable!
+
+          if reflection.polymorphic?
+            raise ActiveRecord::EagerLoadPolymorphicError.new(reflection)
+          end
+          JoinAssociation.new(reflection, build(right, reflection.klass))
+        end
+      end
+    end
+
+    def join_constraints(joins_to_add, alias_tracker)
+      @alias_tracker = alias_tracker
+
+      construct_tables!(join_root)
+      joins = make_join_constraints(join_root, join_type)
+
+      joins.concat joins_to_add.flat_map { |oj|
+        construct_tables!(oj.join_root)
+        if join_root.match?(oj.join_root) && join_root.table.name == oj.join_root.table.name
+          walk join_root, oj.join_root, oj.join_type
+        else
+          make_join_constraints(oj.join_root, oj.join_type)
+        end
+      }
+    end
+
+    private
+      def make_constraints(parent, child, join_type = Arel::Nodes::OuterJoin)
+        foreign_table = parent.table
+        foreign_klass = parent.base_klass
+        join_type = child.join_type || join_type if join_type == Arel::Nodes::InnerJoin
+        joins = child.join_constraints(foreign_table, foreign_klass, join_type, alias_tracker)
+        joins.concat child.children.flat_map { |c| make_constraints(child, c, join_type) }
+      end
+
+    module ClassMethods
+      # Prepended before ActiveRecord::Associations::JoinDependency#walk_tree
+      #
+      def walk_tree(associations, hash)
+        case associations
+        when TreeNode
+          associations.add_to_tree(hash)
+        when Hash
+          associations.each do |k, v|
+            cache =
+              if TreeNode === k
+                k.add_to_tree(hash)
+              else
+                hash[k] ||= {}
+              end
+            walk_tree(v, cache)
+          end
+        else
+          super(associations, hash)
+        end
+      end
+    end
+
+  end
+end

polyamorous/lib/polyamorous/activerecord_6.0_ruby_2/reflection.rb

@@ -0,0 +1,2 @@
+# active_record_6.0_ruby_2/reflection.rb
+require 'polyamorous/activerecord_5.2.0_ruby_2/reflection'